Developer regenerators

ABSTRACT

The present invention provides an aqueous regenerator for addition to an aqueous developer that contains an organic solvent, a dispersing agent and a weak base, and has a pH of between about 8 and less than about 13. The aqueous regenerator includes an organic solvent, dispersing agent, and an effective amount of a strong base such that the regenerator has a greater pH than the developer into which the regenerator is to be added.

BACKGROUND

The art of lithographic printing is based on the immiscibility of inkand water. A lithographic printing plate is composed of ink receptiveregions, commonly referred to as the “image area,” and hydrophilicregions. When the surface of the printing plate is moistened with waterand printing ink is applied, the hydrophilic regions retain the waterand repel the printing ink, and the image area retains the printing inkand repels the water. The printing ink retained on the image area maythen be transferred to the surface of a material upon which the image isto be reproduced. Typically, the ink is first transferred to anintermediate blanket, which in turn transfers the ink to the desiredsurface.

Lithographic printing plates precursors typically include aradiation-sensitive coating applied over the hydrophilic surface of asubstrate. Conventional radiation-sensitive coatings includephotosensitive components dispersed within an organic polymeric binder.After a portion of the coating is exposed to radiation (commonlyreferred to as imagewise exposure), the exposed portion becomes eithermore developable or less developable in a particular liquid than anunexposed portion of the coating. A printing plate precursor isgenerally considered a positive-working plate if, after exposure toradiation, the exposed portions or areas of the radiation-sensitivecoating become more developable and are removed in the developingprocess to reveal the hydrophilic surface. Conversely, the precursor isconsidered a negative-working plate if the exposed portions or areasbecome less developable in the developer and the unexposed portions orareas are removed in the developing process.

After imaging, the precursors are contacted with a developer to removeeither the exposed or unexposed portions of the radiation-sensitivecoating to form a printing plate. This process is generally performedusing a developer system, which is capable of receiving imaged printingplate precursors, and then contacting the precursors with a developereither by spraying the developer onto the precursor or by immersing theprecursor in a developer bath. During development, portions of theradiation-sensitive composition are removed from the precursor to revealthe substrate surface, and portions remain on the plate to provide anink-receptive image. After the developing step, the printing plates arethen washed to remove excess developer.

Suitable developers for processing printing plate precursors may fallwithin at least three general categories defined by the developer's pHrange and whether the developer includes an organic solvent and/ordispersing agent. Each category is effective in developing particulartypes of radiation-sensitive compositions. A first category ofdevelopers includes highly alkaline aqueous developers, generally havinga pH of greater than about 13. These developers utilize the presence ofhydroxyl ions to develop the imaged printing plate precursors. However,these highly alkaline developers do not normally include organicsolvents (e.g. organic alcohols) because the combined activities of thehydroxyl ions and organic solvent may degrade the image area on aprinting plate precursor. Examples of developers falling within thiscategory include ProTherm brand developers and MX 1813 brand developers,both available from Kodak Polychrome Graphics, Norwalk, Conn.

A second category of developers includes acidic to substantially neutraldevelopers, generally having a pH between about 2 and less than 8.Developers falling within this second category contain organic solvents,acids and/or weak bases to control pH activity, and dispersing agents(e.g. organic sulfates or sulfonates) to suspend, disperse or dissolveprinting plate coating materials removed during the development process.These types of developers do not include strong bases. An example of adeveloper falling within this category is the Aqua-Image brand developeravailable from Kodak Polychrome Graphics.

A third category includes developers that have pH ranges between about 8and less than about 13, more particularly between about 8 and about 12.These developers may contain organic solvents, dispersing agents and atleast one weak base (e.g., an organic amine such as ethanolamine,diethanolamine or triethanolamine). An example of a developer fallingwithin this category includes 956 brand developer available from KodakPolychrome Graphics.

During the development of printing plate precursors, the activity of avolume of developer (i.e. the ability of the developer to remove desiredportions of the radiation-sensitive coating to produce an image) mayvary due to the depletion of, or changes in, various components of thedeveloper. For example, over time, the concentration of the organicsolvent or the dispersing agent, as well as the pH of the developer mayvary. Changes in developer activity may be caused by loss of developercomponents as printing plates carry developer out of the developersystem after development. Additionally, interactions with theradiation-sensitive coatings of the printing plate precursors may alsoaffect developer activity. In particular, the pH of the developer maychange due to acid/base interactions with imaged portions ofradiation-sensitive coatings. This loss of developer activity may resultin inconsistency in overall dot density over a cycle of developedprinting plates, which may have adverse effects during printing.

Thus, in certain circumstances, developer activity is been restored,maintained or increased (collectively referred to herein as“maintained”) through the addition of replenishers or regenerators tothe volume of developer. As used herein, the term “replenisher” refersto a substance having approximately the same activity as the developer.Thus, the developer itself is often used as a replenisher to maintainthe volume of developer contained in the developer apparatus. As usedherein, the term “regenerator” refers to a substance having a differentlevel of activity than the developer to which it is added. For example,the regenerator may have a different pH than the developer.

Examples of first category (i.e. highly alkaline) developer regeneratorsinclude 9008 brand regenerator and MX 1919 brand regenerator, bothavailable from Kodak Polychrome Graphics. These regenerators include thesame active components as the developer, but have a higher pH in orderto maintain developer activity. An example of a second category (acidicto neutral) developer regenerator includes Aqua-Image Top-Off brandregenerator, also available from Kodak Polychrome Graphics. Thisregenerator includes a higher concentration of organic solvent anddispersing agent than the developer to maintain activity.

Traditionally, the third category of developers (i.e. containing a weakbase and having a pH between about 8 and less than about 13) did notrequire the use of a regenerator because precise control of developeractivity was not thought necessary to develop a standard cycle ofprinting plate precursors with consistent dot densities. However, recentadvances in imaging technology, as well as a desire to utilize longerdevelopment cycles, have necessitated an increasing level of precisionand consistency in dot density for plates developed by third categorydevelopers. For example, the advent of laser imaging systems hasprovided for more precise imaging than conventional imaging methods.This enhanced imaging precision, in turn, has led to an increase in theuse of stochastic (FM) screening methods in the printing industry.Stochastic screening varies spacing between dots (and optionally dotsize) to create the illusion of continuous tones. In contrast,conventional screening (AM) methods rely on changes in dot size toproduce the illusion of continuous tones. First order stochasticscreening produces dots having the same size, but varies spacing betweenthe dots. Second order screening produces dots with both size andspacing variation. Hybrid screening uses a combination of conventionaland stochastic screening.

Stochastic screening requires precisely controlled dot size, density andspacing in order to create the appearance of continuous tones. However,the activity of third category developers changes sufficiently duringthe development of a cycle of printing plate precursors to adverselyaffect dot density consistency, particularly over extended developmentcycles.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides an aqueous regeneratorfor addition to an aqueous developer that includes an organic solvent, adispersing agent and a weak base, and has a pH of between about 8 andless than about 13. The aqueous regenerator includes an organic solventand a dispersing agent, as well as an effective amount of at least onestrong base such that the regenerator has a pH greater than the pH ofthe developer. In one embodiment, the aqueous regenerator may have a pHof about 12 or greater. The regenerator may also have a greaterconductivity than the developer.

A wide range of organic solvents may be used in the aqueous regeneratorsof the present invention. As used herein, the phrase “organic solvent”refers to an organic substance capable of at least partially dissolving,dispersing or swelling a radiation sensitive material placed in contactwith a developer containing the organic solvent. Suitable organicsolvents include may include an alcohol moiety, for example benzylalcohol, phenoxyethanol, phenoxypropanol and combinations thereof. Theorganic solvent may also include esters of ethylene glycol or propyleneglycol with acids containing alkyl groups of C₁₋₆, or ethers of ethyleneglycol, diethylene glycol or propylene glycol containing alkyl groups ofC₁₋₆. The concentration of the organic solvent may range from betweenabout 1 and about 12 weight percent, more particularly between about 3and about 6 weight percent. Combinations of suitable solvents may alsobe utilized in embodiments of the present invention.

The regenerator may also include one or more dispersing agents. Thetotal concentration of the dispersing agent may be in the range ofbetween about 4 and about 20 weight percent, more particularly, betweenabout 7 and about 15 weight percent. Suitable dispersing agents mayinclude cationic, anionic, nonionic or amphoteric surfactants.Particularly suitable dispersing agents may include a sulfate orsulfonate moiety, for example, alkali metal alkyl sulfates, alkali metalalkylnaphthalenesulfonates, and alkali metal alkylbenzene sulfonates.Examples of particularly suitable surfactants include sodium octylsulfate, sodium methylnaphthalenesulfonate, sodium xylene sulfonate, andsodium toluene sulfonate. The surfactants may be added to theregenerator as an aqueous solution.

Suitable strong bases for use in the aqueous regenerator may have a Kbof about 1 or greater. The concentration of the strong base may rangefrom between about 0.1 and about 5.0 weight percent. Examples ofsuitable strong bases include hydroxides, more specifically metalhydroxides such as sodium, potassium and lithium hydroxide, as well ascombinations thereof.

Optionally, the aqueous regenerator may include a weak base. Suitableweak bases may have a Kb of between about 1×10⁻² and about 1×10⁻⁵. Theconcentration of the weak base may range from between about 0.1 to about5 weight percent. Examples of suitable weak bases include amines, forexample, monoethanolamine, diethanolamine, triethanolamine, or salts,such as sodium carbonate, potassium carbonate, sodium bicarbonate,potassium bicarbonate, trisodium phosphate, tripotassium phosphate orcombinations or derivatives thereof.

In yet another embodiment, the present invention provides a developersystem for preparing printing plates. The system includes a developerunit containing an aqueous developer. The aqueous developer includes anorganic solvent, a weak base and a dispersing agent and has a pH betweenabout 8 and less than about 13. The developer unit is adapted to contactprinting plate precursors with the developer to form an image on theprinting plate. The system further includes a regenerator unitcontaining an aqueous regenerator for addition to the first vessel. Theregenerator includes an organic solvent and a dispersing agent, as wellas an effective amount of at least one strong base such that theregenerator has a greater pH than the developer. The regenerator unitalso is adapted to controllably deliver an effective amount of theaqueous regenerator to the developer unit to maintain the activity ofthe aqueous developer. For example, the aqueous regenerator may maintainthe organic solvent concentration, dispersing agent concentration, pHand/or conductivity of the developer. One or more sensors may beutilized to monitor the activity of the developer.

In a further embodiment, the present invention provides a method fortreating an aqueous developer after developing a portion of at least oneprinting plate precursor. The developer includes an organic solvent, adispersing agent and a weak base, and has a pH between about 8 and lessthan about 13. The method includes the step of adding an effectiveamount of an aqueous regenerator to the developer to maintain theactivity of the developer. The regenerator includes an organic solventand a dispersing agent, and an effective amount of at least one strongbase such that the regenerator has a greater (more basic) pH than thedeveloper.

The pH of the developer may be maintained at between about 8 and lessthan about 13, more particularly between about 9 and about 11, even moreparticularly, between about 9.5 and about 10.5. The organic solventconcentration of the developer may be maintained at between about 2 andabout 8 weight percent, more particularly between about 3 and about 6weight percent. The dispersing agent concentration and/or conductivityof the developer may also be maintained.

In yet another embodiment, the present invention provides a method fordeveloping a plurality of imaged printing plate precursors. A portion ofat least one imaged printing plate precursor is contacted with anaqueous developer including an organic solvent, a dispersing agent and aweak base and having a pH between about 8 and less than about 13. Aneffective amount of an aqueous regenerator is then added to thedeveloper to maintain the activity of the developer. The regeneratorincludes an organic solvent and a dispersing agent, as well as aneffective amount of at least one strong base such that the pH of theregenerator is greater than the pH of the developer. After adding theregenerator, a portion of one or more additional printing plateprecursors may then be developed.

This method may be used to develop printing plate precursors having avariety of radiation-sensitive compositions, particularlyradiation-sensitive compositions that tend to change the pH of thedeveloper. Suitable radiation-sensitive compositions may be laserimageable, and may also include a polymeric material. Suitable polymericmaterials may include acidic or weakly basic functionality such as acarboxylic acid moiety. Specific examples of suitable polymericmaterials include acrylic acid polymers, methacrylic acid polymers orcombinations, derivatives or copolymers thereof. Other suitablepolymeric materials include phenolic resins. In a particular embodiment,the radiation-sensitive composition may be applied in multiple layersonto a substrate. For example, a first layer that is soluble in theaqueous developer may be applied onto the substrate. A second layer thatis not soluble (but is dispersible) in the developer may then be appliedonto the first layer.

In yet a further embodiment, the present invention provides a method offorming a plurality of printing plates. A plurality of printing plateprecursors, each including a radiation-sensitive composition appliedonto a substrate are imagewise exposed to radiation to form a pluralityof imaged printing plate precursors. A portion of at least one of theimaged printing plate precursors is then contacted with an aqueousdeveloper to form a printing plate. The developer includes an organicsolvent, a dispersing agent, and a weak base, and has a pH between about8 and less than about 13. An effective amount of an aqueous regeneratorto maintain the activity of the developer is then added to thedeveloper. The regenerator includes an organic solvent and a dispersingagent, and an effective amount of at least one strong base such that thepH of the regenerator is greater than the pH of the developer. Afteradding the regenerator, at least one additional imaged printing plateprecursor is contacted with the developer to form a printing plate. Inone embodiment, the imagewise exposure step includes the use ofstochastic screening methods and systems.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary developer system ofan embodiment of the present invention.

DETAILED DESCRIPTION

In one embodiment, the present invention provides an aqueous regeneratorfor addition to an aqueous developer that includes an organic solvent, adispersing agent and a weak base, and that has a pH between about 8 andless than about 13. The aqueous regenerator includes an organic solventand a dispersing agent, as well as an effective amount of a strong basesuch that the regenerator has a pH greater than the pH of the developer.

A wide range of suitable organic solvents may be included in the aqueousregenerator of the present invention. Suitable organic solventsgenerally include organic solvents, including the reaction products ofphenol and ethylene oxide or propylene oxide, the reaction products ofesters of ethylene glycol and propylene glycol with acids containingalkyl groups of C₁₋₆, and the reaction products of ethers of ethyleneglycol, diethylene glycol and propylene glycol containing alkyl groupsof C₁₋₆ (e.g. 2-butoxyethanol, or 2-ethoxyethanol). Examples of suitableorganic solvents include phenoxyethanols, phenoxypropanols,phenylpropanols, phenylbutanols, benzyloxyethanols, alkoxybenzylalcohols, benzyl alcohol, and cyclohexanols. The organic solventconcentration may range between about 1 and about 12 weight percent,more particularly, between about 3 and about 6 weight percent.Combinations of these solvents may also be used.

Suitable dispersing agents include anionic, cationic, nonionic andamphoteric surfactants. Examples of suitable surfactants includesulfates and sulfonates, for example, alkali metal alkyl sulfates,alkali metal alkylnaphthalenesulfonates and alkali metal alkylbenzenesulfonates Other surfactants may include polyoxyethylene alkyl ethers,polyoxyethylene alkyl phenyl ethers, polyoxyethylene polystyryl phenylethers, polyoxyethylene polyoxypropylene alkyl ethers, glycerin fattyacid partial esters, sorbitan fatty acid partial esters, pentaerythritolfatty acid partial esters, propylene glycol monofatty acid esters, canesugar fatty acid partial esters, polyoxyethylene sorbitan fatty acidpartial esters, polyoxyethylene sorbitol fatty acid partial esters,polyethylene glycol fatty acid esters, polyglycerin fatty acid partialesters, polyoxyethylenized castor oils, polyoxyethylene glycerin fattyacid partial esters, fatty acid diethanolamides,N,N-bis-2-hydroxyalkylamines, polyoxyethylene alkylamines,triethanolamine fatty acid esters, and trialkylamine oxides, fatty acidsalts, abietic acid salts, dialkylsulfosuccinic acid esters,N-methyl-N-oleyltaurin sodium salt, alkylphosphoric acid esters,polyoxyethylene alkyl ether phosphoric acid esters, polyoxyethylenealkyl phenyl ether phosphoric acid esters, partially saponifiedstyrene/maleic anhydride copolymers, partially saponified olefin/maleicanhydride copolymers, alkylamine salts, quaternary ammonium salts,polyoxyethylene alkylamine salts, and polyethylene polyaminederivatives, carboxybetaines, aminocarboxylic acids, sulfobetaines,aminosulfuric acid esters, and imidazolines. Particularly suitablesurfactants include sodium octyl sulfate, sodiummethylnaphthalenesulfonate, sodium xylene sulfonate and sodium toluenesulfonate. The concentration of each dispersing agent may range frombetween about 0.1 and about 10 weight percent, more particularly,between about 1 and about 7 weight percent. Total dispersing agentconcentration may range from between about 4 and about 20 weightpercent, more particularly, between about 7 and 15 weight percent. Thedispersing agent may be added to the regenerator as an aqueous solution.

Suitable strong bases for embodiments of the present invention may havea K_(b) value of about one or greater. Examples of suitable strong basesinclude hydroxides, more particularly metal hydroxides such as sodium,potassium or lithium hydroxide. Combinations of strong bases may be usedso long as the pH of the resulting regenerator is greater than the pH ofthe developer. The concentration of the strong base may range betweenabout 0.1 and about 5.0 weight percent. The strong base may be added tothe developer as an aqueous solution.

Optional weak bases for embodiments of the present invention may have aK_(b) value of between about 1×10⁻² and about 1×10⁻⁵. Examples ofsuitable weak bases include organic amines such as monoethanolamine,diethanolamine, or triethanolamine. Other suitable weak bases includesodium carbonate, potassium carbonate, sodium bicarbonate, potassiumbicarbonate, trisodium phosphate and tripotassium phosphate. Theregenerator may have a weak base concentration between about 0.1 andabout 5.0 weight percent. Suitable weak bases may be added to theregenerator as aqueous solutions. Embodiments of the present inventionmay also optionally include additives such as thickeners, preservatives,conditioners, chelating agents and anti-foaming agents.

The regenerator of the present invention may be used in aqueousdeveloper systems to maintain the activity of a developer whiledeveloping imaged printing plate precursors. As previously noted,developers lose activity as an increasing number of printing plateprecursors are developed. However, the regenerator of the presentinvention is adapted to maintain sufficient developer activity such thatconsistent dot sizes are observed throughout a development cycle. The pHof the regenerator of the present invention may be at least about 0.5higher, more particularly at least about 0.7 higher, even moreparticularly at least about 1.0 higher than the pH of the developer towhich it is to be added.

In operation, the aqueous developer and regenerator may be used withconventional developer systems. Conventional developer systems mayinclude a developer unit that is adapted to store developer, and toapply developer to printing plate precursors received by the developersystem. The developer may be applied to the printing plate precursors,for example, by contacting the developer to the printing plateprecursors in a developer bath, or by pumping the developer out ofsprayers directed towards the printing plate precursors. Scrubbers mayalso be used as part of the development process. Additionally, thedeveloper unit may include a circulation unit to filter and reuse thedeveloper.

Such developer systems may also include an additional unit that isadapted to house the regenerator and to controllably deliver theregenerator to the developer unit. The additional unit may include ansuitable controllable conduit to facilitate controlled delivery of theregenerator.

An alternate developer system 10 is illustrated in FIG. 1. The developersystem includes a developer unit 15 which applies developer 14 toprinting plate precursors 16. The developer unit 15 includes adeveloping area 12 which receives the precursors 16, brushes 21 to scrubthe precursors 16, and sprayers 38 to apply or contact the aqueousdeveloper 14 to the surface of the precursors 16. One or more guiderollers 18 drive and/or guide the precursors 16 through the developerarea 12. At the exit of the developer unit 15, a water rinse tank 28 isadapted to remove excess developer from the developed printing plate.One or more rollers 22 serve to remove remaining developer 14 from theplate surface 16 before the plate 16 enters the water rinse tank 28. Thewater rinse tank may include one or more sprayers and/or scrubbers, andmay optionally re-circulate spent water through a filter for multipleuses. The developer system may also include a unit at the exit of therinse tank 28 (not shown) that applies a gum or other desensitizer toprotect the surface of printing plate.

The developer unit 15 further includes a circulation unit 30, whichincludes a developer vessel 32, a pump 34 and a filtration system 36.Conduit 31 connects the developing area 12 to the developer vessel 32.The developer vessel 32 is connected to pump 34 via conduit 33. Whenpump 34 is activated, developer is delivered from the developer vessel32, through conduit 35 and filter 36. The developer then flows throughconduit 37 to spray bars 38 in the developing area 12, where developer14 is applied to the printing plate precursor 16. In this manner,developer 14 may be applied to printing plate precursors 16, filteredand then reused to develop additional printing plate precursors 16.

The developer system 10 also includes a replenisher unit 50, including areplenisher vessel 60, which is connected to developer vessel 32 viaconduit 45 that includes pump 44. The replenisher unit 50 is adapted tooptionally deliver replenisher to the developer unit 15 if desired. Thedeveloper system 10 further includes a regenerator unit 65. Theregenerator unit 65 includes a regenerator vessel 70 which is connectedto developer vessel 32 via conduit 55 that includes pump 54. Theregenerator unit 65 is adapted to controllably delivery regenerator tothe developer vessel 32. A standpipe 24 is positioned relative todeveloper vessel 32 so that excess solution in the developer vessel 32may be disposed of. In this manner, the developer system is adapted toadd regenerator and optional replenisher to maintain the activity of thedeveloper. The developer vessel 32 may further include a mixing deviceto expedite mixing of the regenerator and optional replenisher into thedeveloper. The developer system 10 illustrated in FIG. 1 is furtherreported in the United States patent application entitled “DeveloperSystem,” attorney docket 58575-281087, which has the same filing date asthe present application, and is incorporated herein by reference.

There are a variety of ways to provide controlled delivery of theregenerator and optional replenisher to the developer unit 15. In oneembodiment, the development unit includes one or more sensors 39 formonitoring the volume or level of the developer in the developer vessel.If the developer volume or level is too low, the sensors 39 communicatewith the regenerator unit 65 and optionally the replenisher unit 50 tosupplement the developer with regenerator and optional replenisher.Alternatively, sensors 39 may monitor the precursor area that isdeveloped, and then communicate with the regenerator unit 65 andoptionally the replenisher unit 50 to add regenerator and optionalreplenisher to the developer vessel 32 after a predetermined precursorarea or number of precursors have been developed. In another embodiment,regenerator and optional replenisher may be added as a function of thespeed at which the developer system 10 is developing the precursors 16.For example pumps 44 and/or 54 may be set to deliver a volume ofregenerator and optional replenisher at predetermined time intervals. Inyet a further embodiment, one or more sensors 39 may monitor theactivity of the developer 14. For example, sensors 39 may monitor the pHor conductivity of the developer. If the activity varies beyond acertain amount, the sensor 39 communicates with the regenerator unit 65and optionally the replenisher unit 50 to add additional regenerator andoptional replenisher. For example, the sensors 39 may be configured toelectronically communicate with pumps 44 and/or 54 to deliver theregenerator and optional replenisher. Suitable sensor systems areavailable from Oakton Instruments, Vernen Hills, Ill., and include theD.A.M. and Q.D.M. brand systems. An example of a particular pH sensor isthe OAKTON pH/ORP Controller 800 series, available from OaktonInstruments. Although these sensors are described in reference to theprocessor illustrated in FIG. 1, such sensors may be used inconventional processors having a single vessel for adding regenerator.

Combinations of these sensors may also be used to maintain developeractivity. For example, the replenisher may be added to the developervessel 32 after a certain number of plates or total plate area has beendeveloped. However, the regenerator may be added to the developer vessel32 by utilizing a pH sensor that communicates with pump 54 to deliverregenerator when the pH varies beyond a certain level. As is evidentfrom the foregoing, the system 10 does not necessarily deliverregenerator and optional replenisher in the same amounts or at the sametime. Likewise, the system 10 may provide for controlled delivery of thereplenisher and the regenerator in different ways.

Although sensors 39 are described in reference to the developer systemof FIG. 1, similar sensors may be incorporated into conventionaldeveloper systems that include only a regenerator unit and not areplenisher unit. For example, a developer system may include a sensoradapted to monitor the number of printing plate precursors beingdeveloped, and to communicate with the regenerator unit to controllablydeliver a fixed volume of regenerator per square foot of developedplate.

In one embodiment, a sufficient amount of regenerator and optionalreplenisher is added to a volume of developer to maintain the pH of thedeveloper at between about 8 and less than about 13, more particularlybetween about 9 and about 11, and even more particularly between about9.5 and about 10.5. In another embodiment, sufficient regenerator andoptional replenisher is added to a volume of developer to maintain theorganic solvent concentration of the developer at between about 2 andabout 8 weight percent, more particularly between about 3 and about 6weight percent. In yet another embodiment, sufficient regenerator andoptional replenisher is added to a volume of developer to maintain thetotal concentration of the dispersing agent at between about 4 and about20 weight percent, more particularly between about 7 and about 15 weightpercent. In yet a further embodiment, sufficient regenerator andoptional replenisher is added to the developer to maintain theconductivity of the developer at between about 10 and about 40millisiemens, more particularly, between about 10 and about 20millisiemens. The specific amount of regenerator and optionalreplenisher sufficient to maintain developer activity will vary based ona number of factors apparent to those of skill in the art. Such factorsinclude the volume and specific type of developer, the composition ofthe printing plate precursors, the composition of the regenerator, thefrequency of regenerator addition, the activity level being measured,and the surface area of printing plate precursors being developed.Furthermore, at times, the delivery of the regenerator and the optionalreplenisher may increase the activity of the developer above theoriginal activity of the developer without adversely affecting developerperformance. For example, the delivery of regenerator and optionalreplenisher may increase the pH or the conductivity of the developerabove the original pH or conductivity of the developer for a period oftime.

The developer and regenerator reported herein are suitable for use indeveloping a variety of 1-side and 2-sided printing plate precursorsincorporating many types of radiation-sensitive compositions appliedonto a substrate. Suitable radiation-sensitive compositions may be laserimageable, and may include a polymeric material and aradiation-sensitive component. Optional additives include dispersingagents, humectants, biocides, surfactants, viscosity builders, colorants(e.g. acid black), pH adjusters, drying agents, and defoamers, as wellas combinations of these additives.

Suitable polymeric materials for use in the radiation-sensitivecomposition may include acidic or weakly basic functionality (or otherfunctionality affecting the activity of the developer), for example,carboxylic acid moieties. Examples of such polymeric materials includeacrylic acid polymers, methacrylic acid polymers, and copolymers,derivatives and combinations thereof. Such acidic moieties tend toadversely affect the pH of the developer, which, at least in part,necessitates the addition of the regenerator of the present invention.Other suitable polymeric materials may include phenolic resins, forexample novolak resins.

The radiation-sensitive component may be sensitive to ultraviolet,visible, infrared and/or thermal radiation such that the portions of theradiation-sensitive composition that are exposed to the radiation becomeeither more or less developable in a particular developer than unexposedportions of the composition. Suitable radiation-sensitive components arewell known to those of skill in the art, and generally include dyes andpigments. In a particular embodiment, the radiation-sensitivecomposition is laser imageable.

Suitable substrates for the present invention may vary widely dependingupon the desired application and the specific composition employed.Suitable substrates or substrate surfaces may be hydrophilic, and may becomposed of metals, polymers, ceramics, stiff papers, or laminates orcomposites of these materials. Suitable metal substrates includealuminum, zinc, titanium and alloys thereof. In one embodiment, thesubstrate includes aluminum, which may be grained, anodized and/orpost-treated with a suitable interlayer material. Suitable polymericsupports may include polyethylene terephthalate and polyester films. Thesubstrate may be of sufficient thickness to sustain the wear fromprinting or other desired applications, and may be thin enough to wraparound a printing form, typically having a thickness from about 100 toabout 700 μm.

The resulting printing plate precursor may then be imagewise exposed toradiation such that exposed portions of the radiation-sensitivecomposition become either more or less soluble in a developer thanunexposed portions. Suitable types of radiation include UV, IR, visibleand thermal radiation. IR radiation may be particularly useful forembodiments of the present invention. More particularly, suitableprinting plate precursors may be imaged with a laser or an array oflasers emitting ultraviolet, visible, near infrared or infraredradiation in a wavelength region that is absorbed by the element.Infrared radiation exposure, especially infrared radiation in the rangeof about 800 nm to about 1200 nm, may be carried out with a laseremitting at about 830 nm or at about 1064 nm. Suitable commerciallyavailable imaging devices include image setters such as a CreoTrendsetter (available from the CREO Corp., British Columbia, Canada), aGerber Crescent 42T (available from the Gerber Corporation), and ScreenPlaterite Models 4300, 8600 and 8800 (Screen, Rolling Meadows, Chicago).Suitable stochastic screening systems include Staccato brand stochasticscreening available from Creo Corp, and Spekta brand stochasticscreening available from Screen.

Exemplary printing plates precursors, which may be developed withmethods and systems incorporating the regenerator of the presentinvention, are reported in U.S. Pat. No. 6,528,228 to Hauck et al., U.S.Pat. No. 6,555,291 to Hauck, U.S. Pat. No. 6,294,311 to Shimazu et al.,U.S. Pat. No. 6,352,811 to Patel et al. and U.S. Published ApplicationNo. 2003/0129526 to Haley et al., all of which are incorporated hereinby reference. SWORD EXCEL brand plates, available from Kodak PolychromeGraphics are particularly suitable for use with embodiments of thepresent invention. Other suitable radiation-sensitive compositions andprinting plate precursors are reported in U.S. Pat. No. 6,309,792 andU.S. patent application Ser. No. 10/353,106, both of which areincorporated herein by reference.

Adding the regenerator of the present invention to a suitable developermay be particularly useful when developing printing plates that areimaged using stochastic screening techniques. The addition of theregenerator helps to maintain consistent dot densities over adevelopment cycle, in particular, development cycles of substantiallength. The addition of regenerator may also be more cost efficient thanadding replenisher alone.

EXAMPLE 1

A SWORD EXCEL printing plate precursor was image-wise exposed with 830nm radiation, using an internal test pattern on a Creo 3230 Trendsetter(exposure energy=120 mjcm⁻²), available from Creo Products Inc.,Burnaby, BC, Canada. The internal test pattern contained 1, 2, 3, 5, 10,15, 20, 30, 40, 45, 50, 55, 60, 70, 80, 85, 90, 95, 98, 99, 99.5 and 100percent dot images. The image-wise exposure was carried out using bothCreo Staccato (FM) 10 micron and 20 micron screening.

The resulting imaged precursor was developed using an 850 Sword II plateprocessor, an 850 mm processor as supplied by Glunz and Jensen, Elkwood,Va., in the following configuration:

-   -   Developer=956 Developer    -   Developer filter=20 inch, 15 micron wound from Stonehand        (Denver, Colo.)    -   Two plush rollers used in developer tank    -   Processing speed=3.5 ft/min    -   Initial charge of developer=10 gallons    -   Replenisher=956 Developer    -   Developer replenishment rate=2 ml/ft² of plate    -   Regenerator=None

The processor had been recently cleaned and new developer and filtersinstalled. Plate resolution was then measured using a X-Rite 528densitometer (CannonDirect, Bethel, Ohio).

After developing the imaged precursor, 100 square foot increments ofexposed (as above, but with a solid, 100% exposure pattern, in AM mode)SWORD EXCEL plate precursor (“bulk precursor”) was developed through theprocessor to replicate pre-press environment.

After about 1500 ft² of bulk precursor had been developed, another SWORDEXCEL printing plate precursor was imaged, developed and measured forresolution as above.

After about 2200 ft², of bulk precursor had been developed, anotherSWORD EXCEL precursor was imaged, developed and measured for resolutionas above. Resolution for the each printing plate is shown in Table 1.TABLE 1 10 Micron Staccato 20 Micron Staccato Screen Screen Area ofSword Excel Processed Theoretical dot/% 0 ft² 1500 ft² 2200 ft² 0 ft²1500 ft² 2200 ft² 50 47 48 52 46 48 50 60 56 57 62 56 57 59

As demonstrated in Table 1, using 10 micron Staccato screening, dotpercentages varied by 5 and 6 percent, respectively. With 20 micronStaccato screening, dot percentages varied by 4 and 3 percent,respectively.

EXAMPLE 2

Precursors A, B and C, each SWORD EXCEL printing plate precursors, wereimage-wise exposed with 830 nm radiation, using an internal test patternon a Creo 3230 Trendsetter (exposure energy=120 mjcm⁻²), available fromCreo Products Inc., Burnaby, BC, Canada. The internal test pattern foreach precursor included 50 percent dot images. The image-wise exposurefor portions of each plate precursor was carried out using Creo Staccato(FM) 10 micron screening, Creo Staccato (FM) 20 micron screening andconventional (AM) 200 lines/inch screening.

A 7500 square foot (in 100 square foot increments) cycle of bulkprecursor imaged using a 100 percent exposure pattern was developed withan 85 NS plate processor, available from Technical ServicesInternational, Kennett Square, Pa., which was modified to include aregenerator unit as shown in FIG. 1, and an OAKTON pH/ORP Controller 800Series pH sensor (in-line, continuous) from Oakton Instruments, VernonHills, Ill. The processor was further modified to include a standpipe inthe developer vessel (FIG. 1) to maintain a substantially constantvolume. The modified processor was then configured as follows:

-   -   Developer=956 Developer    -   Developer filter=15 micron wound filter (Stonehand, Denver,        Colo.)    -   Processing speed=3.5 ft/min    -   Initial charge of developer=10 gallons    -   Replenisher=956 Developer    -   Regenerator=Regenerator 1

956 Developer is an aqueous developer available from Kodak PolychromeGraphics, which includes a weak base, organic solvent and dispersingagent, and has a pH of about 10. Table 2 below lists the components ofRegenerator 1. TABLE 2 Regenerator 1 Water 601.88 g  Silicone AntifoamAgent - DC Antifoam B - 15%  0.10 g Sodium Octyl Sulfate - 42% 120.50 g Sodium Methylnaphthalenesulfonate - 50% 88.90 g Triton H-66 - 42% 24.00g Diethanolamine - 85% 12.00 g Trisodium Phosphate - 43.12%  9.20 gSodium Hydroxide - 50% 50.00 g p-Toluenesulfonic Acid  0.92 g2-Phenoxyethanol 44.20 g EDTA Tetra Sodium Salt  7.70 g Glycerin - 99.7%40.60 g Total 1000.00 g  pH 13.30 Conductivity (mS) 91.30

DC Antifoam B is available from Dow. Silicone Anti Foam Agent SE 57 isavailable from BYK Chemie, Wallingford, Conn. Triton H-66 is a phosphateester available from Dow.

Precursors A, B and C were developed after 1000, 4000 and 7000 ft²,respectively, of bulk precursor had been developed. During the cycle,replenisher was added to the developer unit at a rate of about 2 ml persquare foot of image precursor that was developed. Regenerator 1 wasadded to the developer as a function of the pH of the developer in thesystem. More particularly, the pH sensor was configured toelectronically communicate with the regenerator pump when the pH of thedeveloper dropped below 9.89. Table 3 shows the amount of regeneratorused during the cycle, which averaged about 2 ml of regenerator persquare foot of imaged precursor. The amount of regenerator used wasmeasured by monitoring volume loss in the regenerator vessel. TABLE 3Square Footage Regenerator(ml)  400 0  800 0 1200 2704 1600 0 2000 02400 0 2800 1217 3200 97 3600 1767 4000 270 4400 1866 4800 0 5200 1685400 826 5600 1723 5800 137 6200 1370 6600 170 7000 461 7400 740 75001325 Total 14841 ml/ft² 1.98

Dot densities for Precursors A, B and C were measured with a GreytagD196 densitometer after development. The results are summarized in Table4. TABLE 4 Staccato 10 Staccato 20 Standard Precursor (Stochastic 10(Stochastic 20 AM (Sq Ft) micron) micron) Screening A (1000) 41% 42% 45%B (4000) 42% 42% 46% C (7000) 43% 44% 46%

The dot densities varied between one and two percent for the threescreening methods, despite operating for three times the cycle length ofExample 1. The dot density variation shown in Table 4 constitutes asignificant improvement over the variation in Example 1, and is anacceptable level of variation in pre-press environment for manycommercial applications.

EXAMPLE 3

Precursors A-O, each SWORD EXCEL printing plate precursors, wereimage-wise exposed as in Example 1, with an internal pattern usingconventional (AM) screening at 200 lines/inch, Staccato (FM) 10screening and Staccato (FM) 20 screening. The conventional screeningpattern included dot densities of 1, 2, 5, 20, 40, 50, 60, 98 and 99percent, as well as 1×1, 2×2, 3×3 and full density. The Staccato 10 and20 screening patterns included 1, 2, 5, 20, 40, 50, 60, 98 and 99percent dot densities.

A 7500 square foot (in 100 square foot increments) cycle of bulkprecursor was imaged and developed as in Example 1, except that noreplenisher was added to the developer. Instead, 5 ml of Regenerator 2per square foot of developed precursor was added to the developer as afunction of the number of precursors developed. The components ofRegenerator 2 are listed in Table 5. TABLE 5 Regenerator 2 Water 738.00g Silicone Antifoam Agent - DC Antifoam B -  0.80 g 15% Sodium OctylSulfate - 42% 67.00 g Sodium Methylnaphthalenesulfonate - 50% 59.00 gTriton H-66 - 42%  3.50 g Diethanolamine - 85% 14.00 g SodiumHydroxide - 50%  7.50 g p-Toluenesulfonic Acid  1.20 g 2-Phenoxyethanol45.50 g Hydropalat 3204 - 50%  7.50 g EDTA Tetra Sodium Salt  9.00 gGlycerin - 99.7% 47.00 g Total 1000.00 g  pH 12.5

Dot densities were measured by developing one of Precursors A-O forevery 500 square feet of bulk precursor developed. Dot densities weremeasured by the densitometer used in Example 2. The results aresummarized in Tables 6-8 for each screening method. TABLE 6 ConventionalScreening Precursor Solid (ft²) 1% 2% 5% 20% 40% 50% 60% 98% 99% 1 × 1 2× 2 3 × 3 Density A (0) 1 2 5 20 40 50 60 99 99 58 53 51 96 B (500) 1 25 20 40 50 60 98 99 59 53 52 97 C (1000) 1 2 5 19 40 50 60 99 99 59 5352 97 D (1500) 0 1 4 19 39 49 60 97 98 59 53 51 97 E (2000) 1 2 5 19 3950 60 97 98 60 53 52 96 F (2500) 0 2 5 19 40 50 61 98 99 60 52 51 97 G(3000) 0 2 5 20 39 49 60 97 98 61 53 51 97 H (3500) 0 1 4 19 40 50 61 9798 61 52 52 96 I (4000) 0 1 4 19 39 49 60 98 98 58 53 52 96 J (4500) 0 14 19 39 50 60 97 98 59 53 52 95 K (5000) 0 1 3 18 39 49 59 98 98 59 5351 97 L (5500) 0 1 4 19 40 50 60 97 98 60 53 51 97 M (6000) 0 1 3 18 4050 59 98 99 59 53 52 97 N (6500) 0 1 4 20 39 49 60 97 98 61 53 52 96 O(7000) 1 1 5 19 40 50 60 97 98 61 53 52 97

TABLE 7 Staccato 10 Screening Precursor (ft²) 1% 2% 5% 20% 40% 50% 60%98% 99% A (0) 0 1 5 20 38 49 60 98 99 B (500) 1 1 4 19 39 50 60 98 99 C(1000) 1 2 5 20 39 49 59 98 99 D (1500) 1 1 5 20 40 50 59 98 98 E (2000)1 1 4 19 40 50 60 97 99 F (2500) 1 2 4 20 41 51 60 98 99 G (3000) 0 2 419 40 51 60 97 98 H (3500) 0 1 5 21 42 50 60 97 98 I (4000) 0 1 4 20 4051 60 98 98 J (4500) 0 1 4 19 40 51 61 97 98 K (5000) 0 2 3 20 40 50 6098 99 L (5500) 0 1 4 20 40 51 60 97 98 M (6000) 0 1 3 19 41 51 61 98 99N (6500) 0 1 4 19 41 50 61 97 98 O (7000) 0 1 4 20 40 51 60 98 99

TABLE 8 Staccato 20 Screening Precursor (ft²) 1% 2% 5% 20% 40% 50% 60%98% 99% A (0) 0 1 5 18 39 50 60 98 99 B (500) 0 2 5 19 39 50 60 98 99 C(1000) 1 2 5 20 40 50 60 98 99 D (1500) 0 2 5 20 40 50 61 97 98 E (2000)0 2 5 19 40 49 61 97 98 F (2500) 0 2 4 19 40 51 60 99 100 G (3000) 0 1 419 40 50 60 97 98 H (3500) 1 1 4 20 40 51 61 97 98 I (4000) 0 1 4 19 3950 61 97 98 J (4500) 0 1 4 18 39 50 59 97 98 K (5000) 0 1 4 19 40 51 6098 98 L (5500) 1 1 4 19 40 50 60 97 98 M (6000) 1 1 4 19 40 50 60 98 99N (6500) 0 1 5 20 40 51 61 97 98 O (7000) 0 1 4 20 41 50 61 97 98

The data shown in Tables 6-8 demonstrate that the use of regeneratorsresults in less overall variation in dot density even over significantlylonger cycle lengths than in Example 1.

1-36. (canceled)
 37. A developer system for preparing printing platescomprising: a developer unit containing an aqueous developer thatincludes an organic solvent, a weak base and a dispersing agent, andhaving a pH between about 8 and less than about 13, wherein thedeveloper unit is adapted to contact printing plate precursors with thedeveloper; a regenerator unit containing an aqueous regenerator foraddition to the developer, the regenerator comprising an organicsolvent, a dispersing agent, and an effective amount of at least onestrong base such that the regenerator has a greater pH than thedeveloper, wherein the regenerator unit is adapted to controllablydeliver an effective amount of the regenerator to the developer unit tomaintain the activity of the developer.
 38. A method for treating anaqueous developer after developing at least a portion of one printingplate precursor, the developer comprising an organic solvent, adispersing agent and a weak base, and having a pH between about 8 andless than about 13, the method comprising: adding to the developer aneffective amount of an aqueous regenerator to maintain the activity ofthe developer, the regenerator comprising an organic solvent, adispersing agent, and an effective amount of at least one strong basesuch that the regenerator has a greater pH than the developer.
 39. Themethod of claim 38 comprising adding an effective amount of theregenerator to maintain the pH or conductivity of the developer.
 40. Themethod of claim 38 wherein the adding step comprises maintaining the pHof the developer at between about 8 and about
 12. 41. (canceled)
 42. Themethod of claim 38 wherein the adding step comprises maintaining the pHof the developer at between about 9.5 and about 10.5.
 43. The method ofclaim 38 comprising adding an effective amount of the regenerator tomaintain the organic solvent concentration of the developer.
 44. Themethod of claim 38 wherein the adding step comprises maintaining theorganic solvent concentration of the developer at between about 2 andabout 8 weight percent.
 45. (canceled)
 46. The method of claim 38comprising adding an effective amount of the regenerator to maintain thedispersing agent concentration of the developer at between about 7 andabout 15 weight percent dispersing agent. 47.-48. (canceled)
 49. Themethod of claim 38 comprising adding an effective amount of replenisherand regenerator to maintain the activity of the developer.
 50. A methodfor developing a plurality of imaged printing plate precursors, themethod comprising: contacting a portion of at least one imaged printingplate precursor with an aqueous developer comprising an organic solvent,a dispersing agent and a weak base, and having a pH between about 8 andless than about 13; adding to the developer an effective amount of anaqueous regenerator to maintain the activity of the developer, theregenerator comprising an organic solvent, a dispersing agent, and aneffective amount of at least one strong base such that the pH of theregenerator is greater than the pH of the developer; and after addingthe regenerator, contacting a portion of at least one additional imagedprinting plate precursor with the developer.
 51. The method of claim 50wherein the printing plate precursor comprises a radiation-sensitivecomposition applied onto a substrate.
 52. The method of claim 51 whereinthe radiation-sensitive composition is laser imageable.
 53. The methodof claim 51 wherein the radiation-sensitive composition comprises apolymeric material that comprises an acidic or weakly basicfunctionality.
 54. (canceled)
 55. The method of claim 53 wherein thepolymeric material comprises a carboxylic acid moiety. 56.-57.(canceled)
 58. The method of claim 52 wherein the radiation-sensitivecomposition comprises an infrared absorbing component.
 59. The method ofclaim 52 wherein the radiation-sensitive composition comprises aplurality of layers applied onto the substrate, including a first layerapplied onto the substrate that is soluble in the aqueous developer. 60.(canceled)
 61. The method of claim 60 wherein the first layer comprisesan acidic moiety.
 62. The method of claim 60 wherein theradiation-sensitive composition comprises a second layer applied ontothe first layer, the second layer comprising a polymeric material thatis not soluble in the aqueous developer.
 63. (canceled)
 64. The methodof claim 50 wherein the at least one imaged printing plate precursorchanges the activity of the developer upon contacting the developer. 65.The method of claim 50 comprising repeating the contacting and addingsteps a plurality of times.
 66. A method of forming a plurality ofprinting plates comprising providing a plurality of printing plateprecursors, each precursor comprising a radiation-sensitive compositionapplied onto a substrate; imagewise exposing the precursors to radiationto form a plurality of imaged printing plate precursors; contacting aportion of at least one of the imaged printing plate precursors with anaqueous developer to form a printing plate, wherein the developercomprises an organic solvent, a dispersing agent, and a weak base, andhas a pH between about 8 and less than about 13; adding to the developeran effective amount of an aqueous regenerator to maintain the activityof the developer, the regenerator comprising an organic solvent, adispersing agent, and an effective amount of at least one strong basesuch that the pH of the regenerator is greater than the pH of thedeveloper; and after adding the regenerator, contacting a portion of atleast one additional imaged printing plate precursor with the developerto form a printing plate.
 67. The method of claim 66 wherein theimagewise exposing step comprises imagewise exposing theradiation-sensitive composition with a laser.
 68. A method of forming aplurality of printing plates comprising providing a plurality ofprinting plate precursors, each precursor comprising aradiation-sensitive composition applied onto a substrate; imagewiseexposing the precursors to radiation using stochastic screening to forma plurality of imaged printing plate precursors; contacting a portion ofat least one of the imaged printing plate precursors with an aqueousdeveloper to form a printing plate, wherein the developer comprises anorganic solvent, a dispersing agent, and a weak base, and has a pHbetween about 8 and less than about 13; adding to the developer aneffective amount of an aqueous regenerator to maintain the activity ofthe developer, the regenerator comprising an organic solvent, adispersing agent, and an effective amount of at least one strong basesuch that the pH of the regenerator is greater than the pH of thedeveloper; and after adding the regenerator, contacting a portion of atleast one additional imaged printing plate precursor with the developerto form a printing plate.
 69. The method of claim 68 wherein thestochastic screening comprises first or second order stochasticscreening, or hybrid screening. 70.-71. (canceled)